Variable contact arrangement for electric coils



March 25, 1969 G. w. POULTON 3,435,396

VARIABLE CONTACT ARRANGEMENT FOR ELECTRIC coILs Filed April 28, 1966 Sheet of 5 UHF] March 25, 3969 G. w. POULTQN 3,435,396

VARIABLE CONTACT ARRANGEMENT FOfi ELECTRIC COILS Filed April 28. 1966 Sheet 2 of 3 March 25, 1969 G. w. POULTON VARIABLE CONTACT ARRANGEMENT FOR ELECTRIC COILS Filed April 28. 1966 sheet United States Patent Ofice 3,435,396 Patented Mar. 25, 1969 3,435,396 VARIABLE CONTACT ARRANGEMENT FOR ELECTRIC COILS George W. Poulton, George St., Industrial Estate, Bridgend, Glamorganshire, Wales Filed Apr. 28, 1966, Ser. No. 546,070

Int. Cl. H01f 29/06; H01c /00 US. Cl. 336-139 12 Claims ABSTRACT OF THE DISCLOSURE An electric coil assembly including a continuous magnetic circuit on the center limb of which a coil is wound. A contact arrangement is mounted within the space between the coil and the outer limbs of the core, the contact arrangement being movable so as to follow the turns of the coil whilst remaining in continuous electrical contact therewith. External electrical connection is made to the coil by way of the contact arrangement.

This invention is concerned with improvements relating to electric coils.

According to the invention there is provided an electric coil comprising a plurality of turns with a magnetic core and at least one contact member constructed and arranged for making continuous electrical contact with the coil, the contact being movable to follow the turns of the coil, and directly or indirectly for making continuous electrical contact with a stationary pick-up member.

The invention will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a half sectional elevation of a transformer according to the invention;

FIG. 2 is an enlarged view of part of FIG. 1 showing further details;

FIG. 3 is a half sectional plan of the transformer illustrated in FIG. 1;

FIG. 4 is an enlarged view of part of FIG. 3 showing further details;

FIG. 5 is a plan view of an alternative drive for the transformer;

FIG. 6 is a side elevation of the alternative drive;

FIG. 7 is an end elevation of the alternative drive;

FIG. 8 is a plan view, part in section, illustrating an alternative contact shoe arrangement for the transformer; and

FIG. 9 is a broken-away side elevation showing the alternative contact shoe.

Referring to the drawings, a core 10 is magnetically connected to a yoke 12 and packets 14 of core iron constituting together with core clamp plates 16 a so-called normal radial type of core. Inner and outer windings, 18 and 20 respectively, are mounted on the core 10. Winding 20 is a single layer coil, and as seen in FIG. 2 is bare of insulation along the outer surface 21. Contact pillars 22, mounted between the core clamp plates 16 in insulating bushes 24, project through the bushes so that they can be joined electrically by a ring 26, arranged not to link the normal radial core, to form a single terminal.

A pair of contact rings 28 encircle the winding 20, upon one turn 30 of which bears a roller 32 free to rotate in, but electrically connected to, rings 28. A toothed driving ring 34 fixed to the rings 28, and with them encircling the winding 20, is in driven contact with pinion 36, which is mounted on a driving shaft 38 so as to rotate with the shaft but to be free to slide along the shaft, which for this purpose is shaped, splined or provided with a long keyway.

The pair of rings 28 is provided with a contact shoe 40, hinged to the ring 28 at 42 and urged outwardly by a spring 44 so as to bear on the contact pillars 22. The latter are equally spaced round the winding 20' and the length of the shoe 40 is slightly greater than the spacing between adjacent pillars 22 so that is any rotary position of the rings 28 the shoe will always be in contact with at least one contact pillar 22. A stop- 46 limits outward movement of the shoe 40. I

In use, the driving shaft 38 is rotated and rotates pinion 36 to drive toothed driving ring 34 which carries round with it the rings 28. This causes rollers 32 to move round the turns such as turn 30 of the winding 20. Electrical connection is thus made from the terminal ring 26, through pillar 22, shoe 40, ring 28 and roller 32, to the winding 20 at its point of contact with the roller 32, which therefore constitutes a continuously variable tapping point of the winding 20.

With designs for some particular sizes of transformer, it is possible to dispense with separate contact pillars and to use the iron packets themselves to pick up contact with the shoe.

While the mechanical drive to rotate the rings has been described with reference to a pinion engaging with teeth on the ring, it could be by a chain engaging with a sprocket. The ring, and in the latter case the chairi, includes an electrical break by means of insulating packing and links respectively to avoid having a short circuited turn constituting a spurious secondary winding. With this break it is not satisfactory to utilise the single driving shaft also as a contact to pick up the current from the rotating ring as each time this break reached the driving shaft the full volts per turn would have to be commutated.

It will be seen that the invention provides a method and device to reduce sparking during variation of the tapping of a coil linked by an uninterrupted core.

When used as a voltage regulator one advantage is the perfectly smooth control of voltage obtained. Another very important advantage is the absence of any limits to the electrical or magnetic design of the transformer or associated circuits such as would be imposed by considerations of commutation of the current from one turn to the next. With known regulators the volts per turn have to be limited to a low value to keep sparking within limits as the contact moves across the turns. With the reduction in sparking of the invention, the contact rollers may be of solid copper and thus able to carry a high current.

The number of contact rollers on one set of rotating rings is immaterial. A continuous sliding turn in contact all the way round would do. A preferred embodiment uses three or perhaps four rollers per set of rotating rings.

While it is possible to have one or more of the rollers of insulating material, serving to support the rings, all the rollers on one set of rotating rings may make electrical contact with the coil. If all rollers do make contact, then as they are all in parallel the current carrying capacity of the regulator is improved. The contact ring is electrically in parallel with the adjacent turn of the winding and connected to it at as many points as there are conductive rollers, so that the ring is electrically identical with the adjacent turn. The moving contact point is then effectively located at the contact shoe on the ring. Thus there must be, for good commutation, only one circumferential position on the rotating rings for the contact shoe which contacts the stationary pillars. Therefore, to improve the current carrying capacity of this contact point, a number of shoe connected electrically in parallel may be placed side by side, successively along the coil. The design of the shoe is not limited to the one shown in the drawing, which is just by way of illustration. A different design or another roller may be used for this purpose.

The arrangement for tapping the coil continuously can equally well be applied to a coil constituting an inductor or resistor, to make the latter continuously variable, though in the form described herein the tapping arrangement is particularly applicable to electricity control apparatus such as voltage or current regulators.

Though the embodiment described above relates to a coil of substantially helical shape its end profile need not necessarily be circular.

It is also possible to keep the rotating rings stationary and to move the coil past the contact rollers.

In a modification, inversion is applied to the design so that the tapping arrangement is within the coil. This then permits the following embodiments.

Two sets of independent rotating rings. are employed, each set with its own independent electrical contact shoe. The contact rollers of one set, as previously described, bear on the outside of the winding helix, while the respective shoe can contact one set of contact pillars. The second set of rings rotates inside the winding helix and the contact rollers of the second set bear on the inside of the coil. The shoe for this second set of rings contacts a second set of contact pillars within the coil. With the two sets of rings rotating in opposite directions a buck and boost feature may be obtained as the rings pass each other in the centre of the coil. It is possible to make the coil for this arrangement in the form of a single spiral, bare on both sides.

In the case of the transformer, the coil tapped according to the invention may be the inner or the outer winding, and in either of these alternatives the tapping arrangement may be inside or outside the coil, giving four embodiments one of which is that described above. Or, more than one coil of a transformer may be tapped as described above.

In any of these embodiments and variations, consequential modifications are made in other parts of the apparatus.

The term single layer coil as used herein is intended to include, where the text admits of it, part of a single layer coil or part or all of one layer of a multi-layer coil, the latter being provided with spacing between the layers for the tapping arrangement when this is between the layers.

FIGS. 5, 6 and 7 illustrate an alternative drive for the contact rings 28. This is a friction drive of a drive ring 48 fixed to the contact rings 28, applied by drive rollers 50, themselves driven by a pair of cooperating spur wheels 52, one of which is driven by a sprocket 54. The latter has applied to it by means of two guide sprockets 56, a driving chain 58.

The sprockets 54 and 56 and the spur wheels 52 are mounted on a carriage 60 freely slidable on two of the contact pillars 22 and provided with a cut-out 62 to allow the shoe to make contact with the pillars. A shaft 64 carrying one of the friction drive rollers 50 at one end and one of the spur wheels 52 at its other end is pivotally mounted on a pin 66 in carriage 60, under the action of a spring 68 arranged to urge the rollers 50 together to increase their grip on ring 48. The compression of spring 58 is adjustable by means of screw 70.

As in the case of the toothed ring drive it is the reaction of turn 30 on wheels 32 that causes carriage 60 to slide along the two guiding contact-pillars 22. Carriage 60 is provided with guide blocks 72 to locate the carriage between the two contact pillars 22, preserve its orientation, constrain it to a longitudinal path and insulate it electrically from the pillars.

FIGS. 8 and 9 illustrate an alternative contact shoe arrangement wherein, by virtue of a lever arrangement, a single spring urges the contact shoe against the contact pillars and tightens the contact rollers against the turn of the winding upon which they rest. In this arrangement, the contact rollers 32 are mounted on the contact rings 28, as before, except for one contact roller 74, which is mounted in the middle of an arm 76 pivoted at one end about a copper tube 78 rigidly clamped between the contact rings 28 (one of which is shown broken away in FIG. 9 to expose the arrangement of arm 76). The contact shoe 80 is shaped to bear on one or two of the contact pillars 22 at only one of its ends, the other of its ends being pivoted freely about the copper tube 78 independently of arm 76. A single spring 82 between the other end of arm 76 and the middle of shoe 80, urges these apart. By reason of the lever action of shoe 80 and arm 76, the force of the spring also urges tube 78 to be pulled away from the turn 30 and thus by way of the contact rings 28, to draw roller 32 towards roller 74 to tighten the rollers against turn 30.

Roller 74 can be replaced by a plurality of rollers, so long only as the set of rollers 74 and the set of rollers 32 are drawn towards one another by the spring 82 to provide better contact with turn 30.

I claim:

1. An electric coil assembly comprising a coil and a magnetic core, said core including a center limb and outer limbs which together with the center limb form a continuous magnetic circuit and said core defining a space between the center limb and the outer limbs, said coil encircling and being secured to the center limb in said space, movable and stationary contact means positioned within said space, means to make external electrical connection to the stationary contact means, and drive means to move the movable contact means to follow the turns of said coil whilst remaining in continuous electrical contact with the said coil and the stationary contact means.

2. A coil assembly according to claim 1 wherein said outer limbs comprise a radially-divided end yoke at each end of said center limb, and a series of axially-extending side yokes connecting the peripheries of the two end yokes to form a radial core.

3. A coil assembly according to claim 2 wherein the movable contact means comprises a conducting roller adapted to roll on the surface of said turns of said coil.

4. A coil assembly according to claim 3 wherein said roller is double-flanged to present a generally semicircular concave surface to said turns of said coil, and wherein said turns of said coil are formed by a conductor which presents to said roller a similar, generally semicircular convex surface.

5. A coil assembly according to claim 4 wherein the movable contact means comprises a conducting ring which encircles said coil with its general plane normal to the length of said center limb of said core, said roller being rotatably mounted on said ring in electrical contact therewith.

6. A coil assembly according to claim .5 wherein at least three such rollers are rotatably mounted on said conducting ring in electrical contact with said ring.

7. A coil assembly according to claim 3 wherein at least one nonconducting roller, otherwise similar to said conducting roller, is rotatably mounted on said conducting ring and rolls on the surface of said turns of said coil to hold said ring spaced from said vcoil.

8. A coil assembly according to claim 5 wherein said conducting ring has an electrical break, so that said ring forms a discontinuous turn around said coil.

9. A coil assembly according to claim 5 wherein said drive means comprises a rotatable shaft extending parallel to the length of said center limb of said core in said space, a flanged pinion keyed to said shaft and slidable therealong, and a toothed ring meshing with said pinion, the toothed ring being associated with said conducting ring so that rotation of said shaft causes said conducting ring to rotate and said roller to follow said turns of said coil.

10. A coil assembly according to claim 5 wherein the stationary contact means comprises a series of conducting pillars disposed around and parallel to the length of said center limb of said core externally of the movable contact means.

11. A coil assembly according to claim 10 wherein said conducting ring carries at least one contact shoe which is maintained in spring-loaded contact with at least one of said pillars as said conducting ring is rotated.

12. A coil assembly according to claim 1 wherein said coil forms one of the windings of a transformer, the other winding of which also encircles and is secured to said center limb of said core.

References Cited UNITED STATES PATENTS LEWIS H. MYERS, Primary Examiner.

T. I. KOZMA, Assistant Examiner.

US. Cl. X.R. 33 8-143 4 

